In the case of molding of a conventional polyester composition at a mold temperature of not more than 100.degree. C., mold release characteristics become inferior because of low crystallization rate. Further, there are problems such as poor dimensional stability and inadequate heat distortion temperature due to insufficient crystallizability.
In order to solve these problems, Japanese Patent Kokoku No. 59-10698 discloses addition of a mono or polyglycidyl ether derivative of a polyalkylene glycol or its monoether to a polyester composition. Japanese Patent Kokai No. 54-158452 discloses addition of a combination of neopentyl glycol dibenzoate and a special nucleating agent to a polyester composition.
However, in these known techniques, molding characteristics at a low temperature are still insufficient and, particularly, in the case of a thin-walled molded product which tends to be cooled quickly, molding characteristics are unsatisfactory. For example, depending upon a particular additive, a composition increases in viscosity and gels or, to the contrary, it decreases in strength due to low miscibility for a polyester, or gas is produced during molding.